Add the new strobe duration and hardware strobe output enable to v4l
uAPI documentation. Additionally add labels for cross-referencing v4l
controls.

Signed-off-by: Richard Leitner <richard.leitner@linux.dev>
---
 .../userspace-api/media/v4l/ext-ctrls-flash.rst    | 42 ++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-flash.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-flash.rst
index d22c5efb806a..7cf0d33e79ff 100644
--- a/Documentation/userspace-api/media/v4l/ext-ctrls-flash.rst
+++ b/Documentation/userspace-api/media/v4l/ext-ctrls-flash.rst
@@ -57,6 +57,8 @@ Flash Control IDs
 ``V4L2_CID_FLASH_CLASS (class)``
     The FLASH class descriptor.
 
+.. _v4l2-cid-flash-led-mode:
+
 ``V4L2_CID_FLASH_LED_MODE (menu)``
     Defines the mode of the flash LED, the high-power white LED attached
     to the flash controller. Setting this control may not be possible in
@@ -80,6 +82,8 @@ Flash Control IDs
 
 
 
+.. _v4l2-cid-flash-strobe-source:
+
 ``V4L2_CID_FLASH_STROBE_SOURCE (menu)``
     Defines the source of the flash LED strobe.
 
@@ -96,6 +100,12 @@ Flash Control IDs
       - The flash strobe is triggered by an external source. Typically
 	this is a sensor, which makes it possible to synchronise the
 	flash strobe start to exposure start.
+        This method of controlling flash LED strobe has two additional
+        prerequisites: the strobe source's :ref:`strobe output
+        <v4l2-cid-flash-strobe-oe>` must be enabled (if available)
+        and the flash controller's :ref:`flash LED mode
+        <v4l2-cid-flash-led-mode>` must be set to
+        ``V4L2_FLASH_LED_MODE_FLASH``.
 
 
 
@@ -186,3 +196,35 @@ Flash Control IDs
     charged before strobing. LED flashes often require a cooldown period
     after strobe during which another strobe will not be possible. This
     is a read-only control.
+
+.. _v4l2-cid-flash-duration:
+
+``V4L2_CID_FLASH_DURATION (integer)``
+    Duration of the flash strobe pulse generated by the strobe source, when
+    using external strobe. This control shall be implemented by the device
+    generating the hardware flash strobe signal, typically a camera sensor,
+    connected to a flash controller.
+
+    The flash controllers :ref:`strobe source <v4l2-cid-flash-strobe-source>`
+    must be configured to ``V4L2_FLASH_STROBE_SOURCE_EXTERNAL`` for this
+    mode of operation. For more details please also take a look at the
+    documentation there.
+
+    The unit should be microseconds (µs) if possible.
+
+.. _v4l2-cid-flash-strobe-oe:
+
+``V4L2_CID_FLASH_STROBE_OE (boolean)``
+    Enables the output of a hardware strobe signal from the strobe source,
+    when using external strobe. This control shall be implemented by the device
+    generating the hardware flash strobe signal, typically a camera sensor,
+    connected to a flash controller.
+
+    Provided the signal generating device driver supports it, the length of the
+    strobe signal can be configured by adjusting its
+    :ref:`flash duration <v4l2-cid-flash-duration>`.
+
+    The flash controllers :ref:`strobe source <v4l2-cid-flash-strobe-source>`
+    must be configured to ``V4L2_FLASH_STROBE_SOURCE_EXTERNAL`` for this
+    mode of operation. For more details please also take a look at the
+    documentation there.

-- 
2.47.3